The is no "Quality" Option on Basic Video Settings (Rendering Problem)

I don't think much of Gif Gun unless you never want to rest on a frame for a while like you would with banner ads with multiple slides.

This is how to create an efficient animated GIF:

Create a new comp with the frame size you need but make sure that it is an even number of pixels wide and tall. I seldom go over 10fps. 15 is the maximum. Buggs Bunny cartoons were only 12 fps, and they look pretty good.

Create your animatiion. If there are parts of the animation where the action stops to give you a good look at something special, like an animated ad banner with multiple slides, keep that animation static for one frame. You will adjust the timing later in Photoshop. When you are finished, trim the comp to the last moving frame. If you want a seamless loop, make sure that the first and last frame of the animation is identical, move back one frame, press "N" to set the work area one frame before the matching frame, and trim the comp to the work area.

Add the comp to the Media encoder and render an animated gif. 

Open the gif in Photoshop. You should automatically have the file set up in the Motion workspace. If it is not, change the workspace. 

You will see a timeline with every frame of the animation. Each frame has a duration that you can change. Go to the at-rest-frame you created and set a new time. Typically for an ad banner, you can set the duration of the hero frames to 10 to 15 seconds. 

I made this gif from the sample AE comp in about 10 minutes. It is only 100 frames long but runs for 16 seconds before looping. It's 1000 X 500 pixels and just over 1 MB.

That is how to create an animated GIF using After Effects. No wasted frames, duplicate frames, no bloated file size.